Abstract: Nucleoid-associated proteins (NAP) play an important role in the maintenance of chromosomal architecture and in global regulation of DNA transactions in prokaryotes. In addition to architectural roles, NAPs are also involved in gene expression and virulence regulation. Bacteria encode multiple NAPs and some of them are essential for survival. Streptococcus mutans, a dental pathogen, encodes one such essential NAP called histone-like protein or HLP. HLP is highly conserved among all the streptococcal species. Streptococcal HLP also appears to be secreted by unknown mechanisms and is highly immunogenic. In these organisms HLP appears to have additional roles such as binding to host cells and involvement in biofilm formation. We and other researchers have shown that streptococcal HLP binds to DNA with a preference for AT rich DNA. Since HLPs are essential for survival in pathogenic streptococci, it is necessary to understand the molecular mechanisms of gene regulation and to identify the HLP regulon. We have recently shown that HLP coordinates gene expression by interacting with CovR, another key global virulence regulator. In this application, we propose to unravel the molecular details of this novel regulatory mechanism mediated by CovR and HLP. Furthermore, we also propose to identify additional genes that are modulated by HLP. We have recently determined the three-dimensional crystal structure of HLP and this will help us with our molecular studies. We hope that the knowledge acquired from this project can also be extended to analysis of other important pathogens such as S. pneumoniae and S. pyogenes, and may lead to the identification of novel drug targets.